1. Field of Invention
The present invention relates to a thermal ink-jet head for recording data by causing heat generated from bubble-producing resistors to produce bubbles in ink and causing the ink to be discharged by the bubble pressure being produced. More particularly, the invention relates to a structure of an ink flow channel in a thermal ink-jet head.
2. Description of Related Art
In order to achieve high operating speeds in recording apparatuses, such as thermal ink-jet printers a repetitive response capability of the ink-jet head is increased. Also, in order to ensure high quality image, ink drops are made to respond to frequency with a certain stability so as to ensure that they reach the surface of a recording paper. In the case that ink drops are jetted unstably, the time required for the ink drops to reach the surface of the recording paper and the direction in which they streak tend to vary widely, thus resulting in lower image quality.
The technology of improving image quality includes increasing density and integration. More specifically, in order to increase image quality the nozzles of the thermal ink-jet head are arranged at a pitch corresponding to dot density. As such, the pitch of the nozzles are decreased. However, when the pitch of the nozzles is adjusted in the above manner, nozzle-to-nozzle crosstalk is created. This crosstalk creates image quality defects as discussed below.
The pressure applied to adjoining nozzles is naturally supplied through a common flow channel behind the nozzles. In order to suppress the crosstalk, bubble pressure of jetting ink is supplied to the nozzle efficiently so as to reduce the pressure supplied through the common flow channel. Therefore, an ink flow channel is preferably structured so that the backward pressure relief from a pressure source is minimized with respect to the nozzle.
Unexamined Patent Publication No. 226978/1994 discloses an apparatus that increases energy directed to the nozzle side by placing a conductance regulating wall in an ink cavity. However, the conductance regulating wall simultaneously interferes with a refill of ink due to an increase in flow channel resistance. This also lowers the response frequency. Accordingly, this combination results in unstable printing.
Another method of suppressing crosstalk is to ease the pressure supplied backward from the nozzle by creating a proper flow channel structure. Unexamined Patent Publications No. 210872/1994 and No. 191030/1994 discloses a buffer chamber with a gas enclosed therein so as to control impedance. However, this structure is complicated and a new instability factor arises from handling gas.
Patent Application No. 307221/1994, discloses a communicating flow channel provided between a nozzle flow channel and an ink reservoir together with grooves extending from a heating element up to the communicating flow channel. The grooves connect the ink reservoir and the communicating flow channel and secure a response capability by promoting a refill of ink. The grooves further catch dust creeping into the flow channel. Accordingly, this apparatus attains a high frequency response capability while also trapping dust. However, this apparatus fails to eliminate the crosstalk because pressure is supplied via the communicating flow channel situated in the rear of a heating element. Thus, by using the apparatus of Patent Application No. 307221/1994, dust has completely been prevented from creeping in the flow channel and the necessity for installing filters in chip flow channels has been eliminated.
Lowering ink flow channel resistance as a method for promoting refill of ink has also been considered. However, printing defects will be produced if the flow channel resistance is significantly lowered. For example, FIG. 16 is a diagram illustrating a dropout defect and FIG. 17 is an enlarged view of a dropout defect portion. As seen in FIG. 16, a dropout defect in the form of a whiteline occurs in the vicinity of the head of a solidly printed portion when solid printing is carried out at a high frequency. As seen in FIG. 17, the appearance of such a white line is caused by the shifting of dot positions. The white line is detected when several dots are shifted in the beginning of printing before dots are stably printed. This mechanism allows the white line to occur when high-frequency printing is performed. Therefore, image quality defects can be avoided by stabilizing the ink flow in the beginning of printing. Avoiding such defects is also accomplishable by putting fluid vibration quickly to the static condition after ink is jetted. In other words, it is possible to decrease the image quality defect by providing sufficient flow channel resistance to suppress the ink vibration. Further, the flow channel resistance is usable for suppressing the backward pressure supplied.
The flow channel structure should be uniformly formed. Unexamined Patent Publication No. 238904/1994 describes a method of uniformly forming a flow channel through a multi-state process. However, by using this design an increase in cost is incurred.
As disclosed in Unexamined Patent Publications No. 155020/1993, No. 183002/1994 and No. 270404/1994, further attempts have been made to improve performance by providing a plurality of kinds of grooves or recesses in a thick-film synthetic resin layer between a channel substrate and a heating substrate. However, in order to have a certain degree of reliability, strict precision is required to form such grooves and recesses. This increases the cost of manufacture.
An object of the invention provides a thermal ink-jet head to improve frequency response capability without causing crosstalk and an increase in manufacturing costs while keeping a chip small in size, and a recording apparatus.
A thermal ink-jet head according to an aspect of the invention comprises a heater substrate having heating elements that produce bubbles and a channel substrate having a plurality of nozzle flow channels, an ink reservoir and a plurality of ink supply ports. The nozzle flow channel is formed in the channel substrate and is disposed above the heating elements and formed up to an end portion of the heating elements. An ink flow channel is at least provided in the heater substrate. The ink flow channel extends from the end of the heating element to the ink reservoir. A sectional area of the ink flow channel increases from the nozzle flow channel to the ink reservoir. A throttle portion is formed in the ink flow channel. The throttle has a smaller cross sectional area proximate to the heating element than the ink reservoir. In embodiments of the invention, the sectional area of the ink reservoir starting from the ink supply port toward the nozzle flow channel may be decreased. Further, the ink reservoir may be used for a plurality of nozzle flow channels.
In embodiments, the sectional areas of the ink flow channel between the end of the heating elements and the ink reservoir may be reduced in the direction in which the nozzle extends. At this time, the nozzle flow channel may have a tilted side extended in a direction perpendicular to the direction in which the nozzle flow channel is orientated and the direction in which the nozzle flow channel is extended. Also, the ink-reservoir-side terminal of the tilted side may be situated above the portion of the ink flow channel where its sectional area is reduced.
According to another aspect of the invention, a thermal ink-jet head comprises a heater substrate having heating elements that produce bubbles and a channel substrate having a plurality of nozzle flow channels. An ink reservoir and a plurality of ink supply ports is also provided. The channel substrate is formed with at least the plurality of nozzle flow channels each extending to the end of the heating elements. The ink supply ports and the ink reservoir are used with the plurality of nozzle flow channels. A sectional area of the ink reservoir communicating with the ink supply ports is increased from the ink supply port toward the nozzle flow channel. A synthetic resin layer is provided on the heater substrate and the heating elements are also provided thereon. A throttle is provided in the heater substrate. The throttle extends from the end of the heating elements to the ink reservoir. A sectional area of the throttle decreases in the direction in which the nozzle flow channel is orientated within the distance from the end of the heating element to the ink reservoir.
According to embodiments, a recording apparatus uses the thermal ink-jet head.
According to embodiments, the sectional area of the ink flow channel is formed with a partition wall between the nozzle flow channel and the ink reservoir formed in the channel substrate. Therefore, the bubble pressure produced on the heating elements acts favorably on the nozzle side since the sectional area of the flow channel proximate to the end of the heating element is minimized, whereby the backward propagation of the pressure can be reduced. As the bubble pressure is efficiently utilized for the discharge of ink drops, sufficient ink-jetting force is secured and the operation is stabilized. Thus improvement in the drive frequency and image quality is accomplishable. Although it is feared that a refill of ink is impeded in the portion where the sectional area is minimized, the ink is only caused to linearly move from between the ink flow channel and the ink reservoir after the bubble dies out as the ink flow channel on the heating element is extended up to the ink reservoir. Consequently, a refill of ink is conducted on the heating element and the ink is resupplied speedily and satisfactorily to ensure a high frequency response capability. Thus the bubble pressure is efficiently used to discharge the ink without impeding a refill of ink by placing the least sectional area portion of the flow channel in the rear of the bubble-producing resistor to provide proper flow channel resistance. Since the ink reservoir side has a sufficient impedance component, not only the attraction of air from the nozzle due to the backward pressure propagation caused after the jetting of ink, but also the disturbance based on the correlation between the rear component of the pressure at the time of high-frequency printing and the bubble-producing pressure is quickly suppressible. Moreover, image quality is made improvable by precisely controlling the dot position as the discharge of ink is stabilized.
Further, even the pressure propagated via the ink flow channel to the ink reservoir is diffused and absorbed into the ink reservoir, whereby crosstalk is reducible. Notwithstanding the provision of the ink reservoir for use common to the plurality of nozzle flow channels, pressure to be propagated to another nozzle is extremely low, so that the influence of crosstalk is obviated.
The aforementioned arrangements are materializable through the conventional process of manufacture only by altering the mask pattern. Therefore, the effects stated above are achievable without any change in cost. As the length of the flow channel is reducible, the number of heads to be laid out per wafer can be increased, which will result in cost reduction. Although a plurality of holes have heretofore been provided in a flow channel corresponding to one nozzle in a heater substrate, only one hole is needed according to the present invention. As a result, not so greater hole-to-hole precision than before is required and this production easier. With the arrangement of providing a synthetic resin layer for a hold as in an aspect of the invention, the thin synthetic resin layer tends to constitute a factor of trouble such as the jutting-out of ink. However, it is intended to minimize an unstable manufacturing factor to decrease the number of holes according to the present invention and this is also led to improving reliability.
With the arrangement of decreasing the sectional area starting with the ink supply port toward the nozzle flow channel in reference to the structure of the ink reservoir as in the second aspect, the diffusion and absorption of the pressure propagated to the ink reservoir are promoted. When the thermal ink-jet head is installed in a recording apparatus, moreover, an ink supply means for supplying ink from an ink tank to an ink supply port is joined to the head. This construction makes it possible to increase the joint area above and form an airtight ink flow channel satisfactorily.
According to embodiments of the invention, the sectional area of the ink flow channel is provided in the heater substrate and extends between the end of the heater element and the ink reservoir and the cross sectional area may be reduced in the direction in which the nozzle is orientated. Therefore, the shape of the bubble produced on the heating elements is regulated in the reduced portion of the ink flow channel while the bubble is growing and the bubble pressure is prevented from being relieved backward, whereby the bubble pressure is efficiently utilizable for ink to be jetted. As the nozzle flow channel has the tilted side extended in a direction perpendicular to the direction in which the nozzle flow channel is orientated and the direction in which the nozzle flow channel is extended, the bubble pressure produced on the heating element can be directed to the opening of the nozzle because of the tilted side with the effect of making the pressure utilizable with efficiency. Further, the ink-reservoir-side terminal of the tilted side is situated above the portion of the ink flow channel where its sectional area is reduced, whereby the sectional area of the ink flow channel is reducible so as to decrease the relief of the bubble pressure toward the ink reservoir. Since the tilted side is positioned close to the heating element or in contact therewith, the bubble can be formed into good shape and the bubble pressure is also efficiently utilizable.
Accordingly, the ink flow channel provided in the synthetic resin layer of the heater substrate contributes to the aforementioned function.
According to other aspects of the invention, the use of the thermal ink-jet head capable of functioning as set forth above makes it possible to put a recording apparatus operating at high speed and offering good image quality to practical use.